Currently tagging is not possible, however you can try to mark some rows as "Processed" by using signals functionality in the action engine.

Thanks for answer, Mateusz!

1) If I use a regular Signal, it will notify "open cases", but not keep visual track of the processed rows, right?

Another workaround would be to try updating an uploaded excel list of items, for which a PQL statement could mark the matching row as "Processed". But then:

2) an excel file cannot be updated, only deleted and another one loaded, right? In this case, could the transformation and data model be unaffected if the file name is the same?

3) is it possible for a User to upload an excel file?